Radiation therapy is a common primary treatment modality for multiple malignancies, including cancers of the head and neck, breast, lung, prostate, and rectum. Depending on the disease, radiation doses ranging from 20 to 70 Gy are often employed for therapeutic use. Diseased tissue and normal organ radiation sensitivities also vary. In order to maximize disease treatment relative to radiation-induced side-effects, various methods of delivery including hyperfractionation (0.5-1.8 Gy), conventional fractionation (1.8-2.2 Gy), and hypofractionation (3-10 Gy) have been explored. These delivery methods explore different regimes of radiation sensitivity in order to maximize tumor cell killing while optimizing treatment times.
Despite obvious advantages with radiotherapy, there can be significant radiation-induced toxicity in tissues. For example, radiation-induced proctitis can be a significant morbidity for patients undergoing prostate or endometrial cancer treatment. For centrally located lung cancer radiotherapy, the esophagus can be incidentally irradiated during treatments, resulting in esophagitis. In the head and neck, radiation of salivary gland or pharyngeal tumors can induce radiation-induced osteonecrosis. Another concern during radiotherapy is the motion of the patient as well as the natural peristalsis of internal organs. These issues highlight the importance of appropriately dosing the cancerous tumors while sparing the normal tissue in order to prevent significant morbidity that arises from radiation toxicity.
Despite several transformative advances since its inception in the late 19th century, radiation therapy is a complex process aimed at maximizing the dose delivered to the tumor environments while sparing normal tissue of unnecessary radiation. This has led to the development of image-guided and intensity modulated radiation therapy. The process of treatment planning requires initial simulation followed by verification of dose delivery with anthropomorphic phantoms which simulate human tissue with more or less homogeneous, polymeric materials. The accuracy of the planning is measured using either anthropomorphic phantom or 3D dosimeters. During the treatment, actual dose delivery can be verified with a combination of entry, exit or luminal dose measurements. Administered in vivo doses can be measured with diodes (surface or implantable), thermoluminescent detectors (TLDs), or other scintillating detectors. However, these detectors are either invasive, difficult to handle (due to fragility or sensitivity to heat and light), require separate read-out device, or measure surface doses only. TLDs are typically laborious to operate and require repeated calibration while diodes suffer from angular, energy and dose rate dependent responses. Although MOSFETs can overcome some of these limitations, they typically require highly stable power supplies. In addition, these dosimeters require sophisticated and therefore, expensive, fabrication processes in many cases. In light of these drawbacks, there is still a need for the development of robust and simple sensors in order to assist or replace existing dosimeters that can be employed during sessions of fractionated radiotherapy.
Radiotherapy along with chemotherapy are still the widely accepted treatment options for cancerous diseases. Over the past twenty years, radiotherapy has undergone major changes including image guided delivery, intensity-modulated radiation therapy (IMIRT), Stereotactic radiosurgery (SRS) and Stereotactic body radiotherapy (SBRT). Along with advancement of sophisticated radiotherapy techniques, the complexity of such procedures has drastically increased. The complex planning process involves numerous individuals enhancing the probability of human error being committed and leading to disturbing outcomes in patient morbidity. One potential solution to avoid such errors is the use of dosimeters to measure and confirm the radiation dose being delivered. Current dosimeters including semiconductor diodes, MOSFETs and Thermoluminescent dosimeters are 1D dosimeters wherein they do not have the capability of rendering a 2D response. To overcome this disadvantage and register spatial dose information led to the development of polymer gel dosimeters. These gel based dosimeters find application during IMRT and SRS treatments. Despite the advantages which warrant their everyday use, these dosimeters are rarely ever used. The biggest limitation preventing their day to day use is the use of Magnetic resonance imaging (MRI) to read the gels which requires highly skilled professionals to perform day to day measurements. For accurate readouts, longer time scans are required which would proportionally increase the cost. In addition, they require complex synthesis protocols including preparation in a fume hood and evacuation of air to prevent oxygen diffusion into the gel. These limitations of the polymer based gel dosimeters make their use highly unlikely on a frequent basis. Taking these into consideration, there is still a requirement for the development of a simple dosimeter which can render spatial information which can be read easily.